Steam or combustion turbines typically operate at extremely high temperatures, for example, 1500° F. to 2000° F. for steam turbines, respective 2500° F. to 2900° F. (1371° C. to 1593° C.) for gas turbines. Such high temperatures can cause failure of various components unless they are protected from the heat. These components include the rotating blades of the turbine, and the vanes for directing gas flow within the turbine. A typical combustion turbine will have three to four rows each of blades and vanes, with approximately 50 to 100 blades or vanes per row, and will typically have approximately 500 total blades and vanes to protect. A commonly used material for vanes and blades is superalloys such as nickel-cobalt. Other turbine components exposed to these high temperatures include the combustor and the transition. These high temperature components are generally insulated by a thermal barrier coating so that the turbine can be operated at such high temperatures without causing excessive deterioration of these components. A typical thermal barrier coating (TBC) is yttria stabilized zirconia.
Currently, it is necessary to periodically stop the turbine and inspect the components for deterioration of the thermal barrier coating, defects in other coatings, or other defects, for example, formation of cracks in the underlying components or spalling of the coating. The surface then heats up in that regions which weakens the superalloy body and causes further spalling of the coating. It would be desirable to monitor the condition of these components while the turbine is in use. Avoiding the need to periodically stop the turbine for inspection reduces downtime, increasing the turbine's efficiency. Likewise, early detection of defects reduces repair costs and outage time, again increasing turbine efficiency. Although other systems of monitoring the condition of turbines during use have been proposed, the present invention provides the unique advantage of providing early detection of defects, and a means of locating the defect; simplifying the inspection and repair procedure once a defect is identified.
An overall monitoring of temperature and strain of the TBC would it make possible to recognize hot spots and mechanical overload. In the past thermocouples and electrical strain gauges were used, which are only single point measurements and the bending of the metal wires limits the use of these sensors only to a few hours.
Therefore there is a need for a method and apparatus for the use of FBG sensors under harsh conditions.